The answer
What is the Medicare Open Enrollment Period?
The term Medicare Open Enrollment Period is used two ways, so it helps to be specific.
Most often people mean the Annual Enrollment Period (AEP), which runs October 15 to December 7 (2026) and lets anyone with Medicare join, switch, or drop a Medicare Advantage plan (Part C) or a Part D drug plan, with changes effective January 1. Separately, the Medicare Advantage Open Enrollment Period runs January 1 to March 31 (2026) and lets people already enrolled in a Medicare Advantage plan make one change, such as switching to another Medicare Advantage plan or returning to Original Medicare. There is also a Medigap Open Enrollment Period, a six-month window that begins when you are 65 or older and enrolled in Part B, during which you can buy a Medigap (supplement) policy without health-based pricing. Knowing which one you mean determines what you can change.